This invention relates to a motion picture film transport and more particularly to an improved film transport in which motion picture film is unwound from the center of a horizontal coil on a first platter and wound onto the exterior of a horizontal coil on a second platter.
Theater motion picture projectors are assembled from several different component parts. These parts include a projection head, a light source, a sound head and a film supply and take-up transport system. Film from a supply coil in the transport system is intermittently advanced past an aperture in the projection head, past the sound head and returned to a take-up coil in the transport system. Various types of film transports have been used in prior art motion picture theater projectors. The most common prior art film transport includes a film supply reel and a film take-up reel. The projection head pulls film from the supply reel at the rate required for normal projection, for example 90 feet per minute, and the take-up reel is driven to wind up the film after it leaves the projection head and the sound head. A system of this type has several disadvantages. The film wound onto the take-up reel is collected on the periphery of the reel so that at the end of the show, the film is in reverse order on the reel. Therefore, it is necessary for an operator to rewind the reel before the next showing. Because of the need for rewinding, two complete motion picture projection systems are needed for continuous operation of a theater. Films are normally shown in segments which are on the order of 20 to 30 minutes in length. While one segment is being shown, the operator rewinds the previously shown segment and then threads the next segment into the projector. With a system of this type, longer film segments are generally not practical since each film reel must be manually loaded and unloaded from the projector and commercial film has considerable weight. As a consequence, a projection room operator must normally be present during operation of a theater.
An improved prior art film transport system is shown in, for example, U.S. Pat. No. 3,661,337 which issued on May 9, 1972 and in U.S. Pat. No. 3,780,959 which issued on Dec. 25, 1973. These patents show a transport system including at least two horizontal platters. The film supply rests in a horizontal coil on a first one of the platters. As a motor rotates the platter, the film is unwound from the center of the coil and delivered to the projection head. The motor speed is varied to maintain a desired film supply rate. A second platter is provided with a core and is rotated by a second motor at a controlled speed for winding the film from the projection head about the core. The film is wound about the exterior of the core to form an increasing diameter coil. At the end of the show, the core is moved from the take-up platter to what was previously the supply platter or to another platter. The operating mode of the two platters then reverses. The second platter, which now carries the coil of film, becomes the supply platter and the film is removed from the center of the coil. A film transport system of this type has several advantages over a reel-type transport in that an entire film may be positioned on the transport system. This eliminates the need for changing reels during the show. Furthermore, since the film is removed from the center of the coil on the supply reel, the need for rewinding the film is eliminated. As a consequence, the projection room operator only need be present before the show for threading the film and starting the projector. However, prior art transport systems of the type using the horizontal platters have been complicated and expensive. The use of a separate motor for each platter and separate sensors for controlling the speed of each motor not only increases the expense, but also increases the chances of component failure.